1. Technical Field of the Invention
The present invention relates to a technology for estimating a pitch (fundamental frequency) of music sounds.
2. Description of the Related Art
A technology for estimating the fundamental frequency of a desired sound (tone) included in music sounds (which will be referred to as a target sound) is described in Japanese Patent Registration No. 3413634. In this technology, an amplitude spectrum or power spectrum of a target sound is modeled as a mixed distribution of a plurality of tone models, each of which is a probability density function modeling a harmonic structure, and a distribution of respective weights of the plurality of tone models is interpreted as a fundamental frequency probability density function, and a salient peak prominent in the probability density function is estimated as the pitch of the target sound.
However, a number of peaks appear in the fundamental frequency probability density function at fundamental frequencies other than the fundamental frequency of the desired sound. For example, peaks in an amplitude spectrum of a sound whose fundamental frequency is 100 Hz overlap at the harmonic frequencies (200 Hz, 400 Hz, 600 Hz, 800 Hz, . . . ) with peaks of another amplitude spectrum of another sound whose fundamental frequency is 200 Hz. Thus, when a sound whose fundamental frequency is 200 Hz is included in a target sound, a salient peak appears not only at 200 Hz but also at 100 Hz in its fundamental frequency probability density function even though no sound of a fundamental frequency of 100 Hz is actually included in the target sound. In addition, when the target sound is a mixture of a number of sounds, prominent peaks corresponding to fundamental frequency and harmonic components of the sounds appear in the fundamental frequency probability density function. It is difficult to accurately extract only the fundamental frequency of a desired sound from such a probability density function which includes a number of salient peaks.